A wide variety of improvements have been made in recent years in the eyewear field, particularly with respect to eyewear intended for use in active sports or as fashion sunglasses. These improvements have been incorporated into eyewear having a unitary lens, such as the "Blades.RTM." design (Oakley, Inc.) the "M Frame.RTM." line (Oakley, Inc.), and the "Zero.RTM." line also produced by Oakley, Inc. These eyewear designs accomplish a variety of functional advantages, such as maximizing interception of peripheral light, reducing optical distortion and increasing the wearer's comfort level, compared to previous active sport eyewear.
The unitary lens of the "Blades.RTM." eyewear incorporates the cylindrical geometry disclosed, for example, in U.S. Pat. No. 4,859,048, issued to Jannard. This geometry allows the lens to closely conform to the wearer's face and intercept light, wind, dust, etc. from directly in front of the wearer (anterior direction) and peripherally (lateral direction). See also U.S. Pat. No. 4,867,550 to Jannard (toroidal lens geometry).
Although the early unitary lens systems provided a full side-to-side range of vision and good lateral eye protection, the potential for optical distortion still exists. In a unitary lens system, for example, the angle of incidence from the wearer's eye to the posterior lens surface changes as the wearer's sight line turns in the lateral direction. This results in disparate refraction between light entering closer to the front of the lens and peripheral light entering at the lateral ends. To address this source of prismatic distortion, U.S. Pat. No. 4,859,048 discloses tapering the thickness of the lens from the medial portion toward the lateral edge.
Prior art eyewear has also employed dual lens systems in which two separate lenses are mounted along a front frame. In the early dual lens eyeglass systems, each of the right and left lenses were roughly co-planar in the as-worn configuration. Thus, the sight line of the wearer, when looking straight ahead, generally crossed the posterior surface of the lens at a normal to the lens surface in the optical zone. One of the disadvantages of this lens configuration was that the eyeglasses provided essentially no lateral eye protection without the use of special modifications, such as vertically elongated earstems or side attachments.
Dual lens systems were thereafter developed in which the lateral edge of each lens curved rearwardly from the frontal plane, and around the side of the wearer's head to provide a lateral wrap similar to that achieved by the high wrap unitary lens systems. Although the dual lens eyeglasses with significant wrap provided lateral eye protection, the lens curvature generally introduced measurable prismatic distortion through the wearer's angular range of vision. This was particularly pronounced in lenses comprising low index of refraction materials. In addition, although high base curvatures (e.g. base 6 or higher) are sometimes desirable to optimize wrap while maintaining a low profile, such lenses have not been practical in the past due to the relatively high level of prismatic distortion.
Thus, there remains a need for a high base nonprescription lens for use in dual lens eyewear which can intercept light over essentially the full angular range of vision while at the same time minimize optical distortion throughout that range.